Equalizing drive for conveyer systems



March 1, 1932. J. B. WEBB ET AL EQUALIZING DRIVE FOR CONVEYER SYSTEMS Filed March 18, 1930 1H4 b- "rm/s 75.Webb,Duanc /9.

4 Sheets-Sheet 2 (198 fll/l/ INVENTORS 751aand Char/es f). Sink ATTORNEY.

March 1, 1932. J. B. WEBB ET AL 1,847,152

EQUALIZING DRIVE FOR CONVEYER SYSTEMS Fileq March 18, 1950 4 Sheets-Sheet 5 J W Mum W and Charles A. Sin

BYMW

A TTORNE Y.

March 1, 1932. J. B. WEBB ET AL 1,847,152

EQUALIZING DRIVE FOR CONVEYER SYSTEMS Filed March 18, 1950 4 Sheets-Sheet 4 a o o o o O 9 I N VEN TORS A TTORNEY.

Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE J'ERVIS 3.. W133,

OF ROYAL OAK, DUANE A. BLAIR, OI DETROIT, AND CHART-um A. m

01 IONTIAO, MICHIGAN EQUALIZING DRIVE FOB CURVE YER SYSTEMS Application fled latch 18, 1830. Serial Io. 436,888.

This invention relates to conveyer systems of the type which has comparatively recently come into extensive eneral use in manufacturing plants for modern high speed produc- 5 tion methods of manufacturing, and wherein a continuously operating endless chain conveyer transports articles from one part of a manufacturing plant to another and during which transportation various processing and manufacturing operations are performed by workmen located at various stations along the conveyers line of travel. One of the most important advantages in the use of such conveyer systems is that the speed of travel of the conveyer may be employed to regulate with marked accuracy the desired or predetermined rate of production, the conveyer acting as a pa'cemaker for all the workmen no matter how difierent each mans particular work may be from others. In view of the fact that the entire production of a plant is in many instances dependent upon the operation of the conveyer it is of the utmost importance that the conveyer shall continue to operate without interruption, and that breakage of the conveyer chain, or other accident, be, if possible, entirely obviated, or at least the number of such accidents be reduced to a minimum. As the main conveyer lines, of systems of the type disclosed, are usually hundreds of feet in length, it has been found that the driving load for a very long conveyer is too excessive to be carried by a single drive and that it is highly desirable to employ for such long conveyer lines several drives located at intervals along the conveyer. While the use of a plurality of drives, located at spaced points, overcomes the objection. to concentrating the entire driving load on a single drive, it introduces other problems, the solutions of which have proven very difiicult. Among such problems may be noted that of securing proper synchronism of the speed of the plurality of drives. Moreover it has been found that even when the desired speed synchronism has been secured, another difiicult problem is introduced, namely that of proper compensation for variation in the length of different sections of the conveyer chain. It 60 will be readily understood, that although these conveyer chains are constructed of standardized parts, all of as nearly uniform and accurate dimensions as ossible to secure, the fact that each chain, 0 several hundred feet in length, consists of thousands of links, makes it impossible to obtain exactl uniform lengths for each chain section 0 say one thousand links. Again, as it frequently may occur, a conveyerchain may jam at a certain point, thereby placing a strain on the links or their connect1ons,wh1ch results in a lengthening of a chain section without breaking any of the parts thereof. While the use of a plurality of drives has many advant es over a single drive, it has been found t at the variations in the len h of different sections of the conveyer chain will at times tend to throw the entire driving load on but one or two ofthe driving units, and such units, in addition to having the entire driving load thrown upon them must also exert their power through the driving connections to the chain of the other drives which for the time are not exerting any driving influence.

The principal'object of the present invention is to rovide a new and improved construction or a conve er of the t e above set forth by means 0 which the difiiculties above recited are successfully and satisfactorily overcome.

Another object is to provide a plurality of conveyer drives, each of which is automatically responsive to variations in the load respectively thrown upon it, thereby to efiect an equalization and distribution of such load to the other drives.

A further object is to provide a plurality of conveyer drives, each of which includes a change speed device and means for adj ustin said device automatically in accordance wit variations in the load so as to insure a substantially uniform load upon each drive.

Another object is to provide a plurality of conve er drives, each of which includes a varia le speed driving device capable of being manually adjusted as desired and also including means automatically responsive to variations in load.

The above and other objects of the invention will appear more fully from the following more detailed specification and bfy referwill hereinafter be pointed out more fully. ence to the accom anying drawings orming The present invention relates more specifica 9. art hereof an wherein:

ig. 1 is a plan view, partly in section,

of a drivin unit for a conveyer, of the type above set orth, and constructed in accordance with the principles of the present in vention.

Fig. 2 is a side elevation of the structure shown in Fig. 1. I

Fig. 3 is a section on the line 3-3 of Fig. 1.

Fig. 4 is a plan view of a stationary supporting frame for a driving unit. v

Fig. 5 is a plan view, partly in section, of a movable frame member which sets within and cooperates with the frame of Fig 4.

Fig. 6 is a transverse section through the .pair of frame members showing them in associated position.

Fi 7 and 8 are enlarged sectional details on t5: lines 77 and 88 respectivelyof Fig. 1.

Fig. 9 is a fragmentary plan view showing a modification of the invention in which an electric switch is employed for controlling the s ed of rotation of a conve er driving unit in accordance with the load conditions and Fig. 10 is a diagrammatic plan view of a conveyer system which includes a pluralitypf driving units constructed in accordance wlth the invention.

In order that the basic principles of the present invention will be more thoroughly understood reference will first be made to the diagrammatic showing of Fig. 10. In this figure the reference character 11 indicates an endless conveyer chain of the type hereinbefore referred to and which conveyer chain may be assumed to be several hundred feet in length and may travel in a path of any desired outline about a manufacturing plant. The rectangular path of travel of the chain. 11 shown in Fig. 10 is merely dia rammatic and obviousl is not intended to epict any actual instal ation or to in any way define the limits of the present invention. As hereinbefore pointed out the 'endlesschains of conveyer systems of the type herein under discussion are of such' great length that it is highly desirable to employ a number of driving units placed at spaced intervals about the conveyers line of travel. In Fig. 10, four of such units. are indicated and are'generally designated by the reference characters M, A1, A2, A3. Each of these driving units includes a driving member, known in the art as a caterpillar drive, and which consists of an endless chain 12 trained about a pair of sprockets 13 14. The driving unit M ma be considered as the master drive for the chain 11 and the units A1, A2, A3 auxilia drives. All of the units M, A1, A2,,A3, are of the same general construction with certain exceptions as to the master drive M which .ing of that section, w

(11y to constructional features of the auxiliary rives A1, A2, A3 which will presently be described. I

As hereinbefore pointed out variation in the len hs of different sections of the conveyer c ain will at times tend to throw the entire driving load on but one or two members of the plurality of drives. For example that section of the chain which extends, considered in the direction of the arrows, from thedriving unit A2 to the master drive M in Fig.,10 may, at some time in the operation of the conveyer, have been sub'ect to an undue strain thereby roducing a lengthenereas the section extending from the master drive M to the driving unit A2 may have remained of substantially the same length as it was at the time of the original installation of the chain. Un-

der such circumstances it will be readily understood that the upper half of the chain, that is the part extending from the master drive M to the drive A2 will be under tension and the full driving load will be thrown upon the driving units A1 and A2. Slack in the chain due to the greater length of the section thereof between the driving unit A2 and the master drive M prevents the driving unit A3 andthe'master drive M from exerting any driving force. Again it will be readily understood that the section of the chain between the drive A1 and the drive A2 may be shorter than the remaining sections so that the entire driving force would have to be exerted by the one driving unit A2. Under any of the above conditions excessive strain is naturally placed at times u on the various driving members. To avoi such excessive strains the construction now to be described has been invented.

By referring to Figs. 1 and 2 which show respectively in plan and in side elevation one of the drivin units A1, A2 or A3, it will be seen that-'eac unit consists of a main supporting frame 15 ofrectangular configuration. This frame is shown most clearly in Fig. 4 of the drawings and is supported, as shown in Fig. 2, from the ceiling or any suitable supporting structure by the standards 16. The frame 15 is preferably constructed of a lurality of angle irons, the leg'sor webs or w ich are arranged to form a horizontal sup orting surface 15A and a verticall Jxten 'ng peripheral flange 15b. The fra e 15 is held in stationary position by the standards or brackets 16 as will be readily under-. stood. Mounted within the stationary frame y 15 is a movable frame 17 .also of rectangular configuration. The frame 17 includes a pair ry of side rails 17a and 17b also preferably constructed of angle irons. Mounted between the side rails 17a and 17b and holding them in spaced relationship is a pair of end rails 170 and 17d and intermediate or transverse rails 17c and 17 f. The end rails and transverse members are referably. constructed of suitable structural 11011 such as I beams.

, Interpomd between the frames 15 and 17 are a plurality of anti-friction rollers 18-19. The rollers 18 are mounted to rotate upon vertically extendin axes and are supported upon bolts 20 exten g between the horizontally extending webs of the side rails 17a- 17b of the frame 17 and the horizontal webs of short pieces of angle iron 21 suitably secured to the side rails 17a-17b. The rollers 19 are mounted to rotate upon horizontally u extending axles or bolts 22 extending between the vertical webs of the side rails 17a, 17b and of the angle irons 21 for supporting said rollers 19 all as clearly shown in Figs. 2, 5, 7 and 8 of the drawings.

Mounted u on the movable frame 17 is a base 23 whic may be of any suitable construction, but which preferably is in the form of a castlng having a horizontal peri heral flange 23a which serves as a means or securing the base 23 to the frame 17; in the example shown, bolts-24 pass through the flange 23a and are screwed into the up er webs of the transverse members 17e 7f. Suitably secured to the base 23 is a reduction gear 25, the driving shaft 26 of which has its outer end suitably supported in a bearing bracket 27. Secured to the shaft 26 is a beve pinion gear 28, the teeth of which mesh with a bevel gear 29. The latter issecured to the u u per end of a vertically extending shaft 30 w ich pro ects through suitable bearings provided in ghe base 23.and has secured to its lower end a spur pinion gear 31.

Meshing with the teeth of the pinion gear 31 is a driven gear 32 rotatably mounted upon a stub shaft 33 suitably anchored in the base 17. The driven gear 32 has fixed to it, preferably by safety shear pins 33, the driving sprocket 14 so that the sprocket 13 and gear 32 will rotate together as a unitary structure. As shown'in Fig. 1 and in the dia ammatic view of Fig. 10 the chain 12 is riven by the sprocket 14. The axes of the sprockets 13-14 mtersect a line which is inclined to the line of travel of the main conveyer chain 11. The sprocket chain 12 has pivotally secured to it a plurality of driving dogs 34 of well known construction which insure that the pressure exerted by the caterpillar chain 12 in driving the main conveyer chain 11 will always be substantially normal to the. contactin faces of the members of both chains at their points of contacting drivin engagement. As will best be understood y referco ring to Fig. 10, the dogs 34 of the caterpillar chain 12 will pass into meshing engagement able the pur caterpil ar drive c ain 12. For the puit'lpose pod travel towards the companion s rocket 14, for-the chain 12, they will gra ually pass out of engagement with the links of the 011- I veer chain 11.

ach sprocket 13 is rotatably mounted upomw a stubshaft 35 similar to the shaft 33 herembefore referred to. Each shaft 35 is non-rotatably secured adjacent to its u per end in a slide plate 36 shdabl moun in a suitslida le mountin of the s rocket 14 is for of a 'usting t e tension in the of securing the slide plate 36 in adjuste sition each slide plate has swivelly en with it the end of an adjusting bolt. 38 which passes through the vertical web for the ad- ]acent transversely extending frame member 176. The bolt 38 is provided with a usual hexagon head 380 or other suitablemeans for enabling the bolt to be readily rotated; lock nuts 3940 are rovided u on the adjusting bolt 38 for ho ding said 7 It and its slide 36 in adjusted position.

, The movable frame 17 as hereinbefore pointed out is mounted within the main supporting or stationary frame 15 and is normally urged towards one end of the frame 15 by the following means: A pair of bolts 41 pass freely through suitable apertures provided in the vertically extending web 15b of ideway 37 forms in the base 23. This one of the end rails of the frame 15 and also through a similar aperture provided in the central web of the end rail 17 d of the frame ly out o engagement with the links of the conveyer chaln 11 each frame 17 has secured thereto a guide rail 45 which is supported from the frame 17, in depending relationship thereto, b means of a plurality of brackets 46, and t e guide rail 45, as most clearly shown in Figs. 2 and 5, is positioned in horizontal alignment with the main conveyer chain 11 and extends along said chain for a length thereof slightly greater than the length of the conveyer chain with which the dogs of the caterpillar chain are at any time in engagement.

Secured to the input shaft of the reduction gear 25 by any suitable means, such as a flexible coupling 50, is a driving or output shaft 51 of a variable speed driving device which 56 locat 1 I, pulleys may be shifted axially-relatively to its 000 rating pulley member. An endless belt or c ain54 is trained about the pairs of pulleys 52-53 and the movable member of each pair of pul which'is ivotally mounted upon a fulcrum v mid way between the'axes of rotation of the pairs of pulleys'52, 53. The arrangement is such that when the lever 55 isv rotated u on its fulcrum 56 the movable member of (mo pair of pulleys will have imparted to it a movement towards or from its coopcrating pulley member equal in extent but opposite in direction to the movement of the movable member of the other pair of pulleys. This arrangement results in securing tion the pulley members and lever 56-are suitably mounted upon a rectangular frame 57 which in the particular constructional example herein illustrated is suitably supported .u on the base 23.

One end of the lever 55 projects beyond the pair of pulley members 53, and has secured to it a nut 58 in threaded engagement with screw threads formed upon a shaft 59. The shaft 59 has its ends journaled for rotation within suitable. bearing brackets 60, 61, and hassecured upon its end a bevel gear 62 which meshes with a similar gear 63 suitably secured to the end of a shaft .64. The shaft 64 carries a pinion 65 which meshes with a rack 66, supported u on bracket 67 secured to the stationary ame by means of braces 68. Fixed to the outer end of shaft 64 is a hand wheel 69 by means of which the Reeves drive may be manually set.

Pinion 65 is non-rotatably but slidably secured to the shaft 64'and is provided with an extension having an annular groove 65a theretion to hold the pinion 65 in meshing engage ment with the rack 66.

Trained about a sprocket 72, secured to the input shaft 73 of the Reeves-drive, and also about a sprocket 74 secured to the armature .shaft of an electric motor 75 is a-sp'rocket chain 76, which in co-operation with its sprockets 72, 74 forms the driving connection from the electric motor to the Reeves drive.

leys has secured to it-a lever The'master drive M is similar in tion to the auxiliary drives A1 A2 A3 except that it is not provided with the sprin pressed movable frame 17 nor with the rac 66 and pinion arrangement such as associated with the auxiliary drives.

The manner in-which the device as hereinbefore described operates is as follows:

The adjustin device for the Reeves drive of the master riving unit M as well-as the 'u stin devices for each o theauxiliary (lllVlIl evices, is adjusted to secure as nearly uni orm drivin conditions at the desired speed as possible a er which the electric mo- .tors 75 for the driving units are ener 'zed,

the control of said motors preferably eing secured by means of 'a single main or master switch. 1 4

In setting the auxiliary drives, the stop pin 71 is removed and lever is actuated to slide the pinion 65 laterallyl alon its shaft 64 out of engagement with t e rac 66, after which the hand wheel 69 is rotated to produce through. gears 62, 63 and shaft 59 the desired adjustment, after which the pinion 65 is again placed in mesh with rack 66.

The motors of all of the driving units bein energized their rotation will be commumcated through the sprockets 74, 72 and chain 76 to the input shaft 73 of the Reeves drive, thence through said drive to the input shaft of the re uction gear 25, through said gear to the shaft 26, bevel gears 28-29 to shaft 30, inion 31 and gear 32. As gear 32 is rotate it. carries with it the driving sprocket 14 for the cater illar chain 12, the

dlrection of travel of sai chain being as indicated in Fig. 10. As the dogs 34 of the chain pass around the sprocket-'13 they will engage between the links of the conveyer chain 11 and cause the same to be driven in the direction of'the arrows in Fig. 10. It will be obvious from an inspection of Fig. 10 that the reaction. upon the caterpillar chains willbe in a direction opposite to the direction of the drive and conse uently if, due to any of the causes herein efore' set forth, too heavy a load is placed upon any one of the auxiliary drives, for example, the driving unit A1, its frame 17 will yield against the action of the springs 42, said frame moving rearwa'rdly or to the left in Figs. 1 or 10. This movement of the frame 17 will be relatively to the frame 15, the latter being stationary, and a rolling or rotation of the pinion 65 upon the rack 66 will occur, thus producing a rotation of the shaft 64 which will be communicated through the bevel gears 63, 62 to the threaded, shaft 59 in a direction such as to cause the Reeves drive to be adjusted to reduce the speed of travel of the caterpillar chain 12 of the drive A1. .The springs 42 are adjusted to permit the above described movement of the frame ,17 relatively to the stationary frame 15 Ill Leanna whenever the pressure orload thrown-upon the chain 12 carried by the respective frame 17 exceeds a certain predetermined amount according to the particular design or installation. The backward movement of the frame 17 in combination with the automatic reduction of speed of its chain 12 will quickly reduce the driving efiect of said cha1n,as will be readily understood, until the driving effect of or pressure reaction-on, the chain is brou ht below the predetermined amount. When t is return will cause the control oradjusting means of the Reeves drive to be actuated in a present invention, and moreover as they are a standard commercial article the details direction reverse to that above described to bring about an acceleration of the s eed of the chain 12. It will be seen from t e foregoing that each auxiliary driving unit will e, as it were, in a balanced condition, being automatically decelerated or accelerated in accordance with variations in the load thrown upon it. As the master drive M however is not made responsive to such load variations its set or adjusted speed of travel will remain unaltered, consequently teration of theset spec and its speed will remain uniform in accordance with the setting of the master drive.

In Fig. 9 of the drawin is shown a modified construction in whic the movement of the movable frame 17 is used to actuate a limit switch 80. As the constructional detailsof such switches form no part of the thereof have not been shown in the drawings. The switch'illustrated is of the type wherein the switch actuating arm 81 is pivotally mounted at its upper end in the switch casing and is provided at its lower end with an antifriction roller 82. This roller lies in the path of movement of a part of the movable frame 17 as shown, the frame carries an adjustable screw 83, having at its end a plate 84 adapted to engage the roller 82. The lower end of the switch arm 81 is normally urged by a suitable spring (not shown) which forms a part of the commercial limit switch, towards the right in Fig. 9. When the frame 17 is caused, by an excess load, to move towards the left the plate '84 will engage with the roller 82 and throw the switch 80 to cause the circuit to its motor to be broken, thus stopping the motor. Stoppage of the motor will immediately cause the driving effect of the chain to cease, thus permitting the frame 17 to be moved towards the right by the springs 42, the plate 84 moving with the frame allowing the switchv arm 81 to move to the right and as soon as the frame returns to its predetermined normal operating position the switch will close the circuit to its motor 7 5 theree retuuned to its.

there will be no a1- of the conveyer chain a by placing the driving unit in operative driv- 1n relationshi to the conve er chain.

, e limit switch shown in i 9 may also be used in combination with the ves drive construction shown in .Figs. 1-to 3 inclusive of the drawings in which case said switch will be em loyed as a safety device and the'plate 84 wil be adjusted to cause the limit switch to be opened when the'springs 42 are compressed to their fullest extent.

It will be seen from the foregoing descri tion that in both forms of the invention the frame 17 of each of the auxiliary-driving units is moved automatically in response to variations in the load placed upon the respective caterpillar chains and that such movement of the said frames is employed to cause deceleration and acceleration of the driving speed of said caterpillar chains.

The herein isclosed have been selected merely as illustrative of the principles of the invention and not as limitm the invention to the specific details selectec l for illustration, it will therefore be understood that man chan es,- variations and modifications of suc detai s may be resorted to without departing from such principles, for example, although a Reeves drive has been shown and described as the variable speed transmission employed it will be obvious that the invention is not limited to this specific type of transmission but as hereinbeforepointed out any suitable variable speed driving device ma be'used.

e claim:

1. The combination witha continuous conveyer of a plurality of driving units located at. spaced intervals along said conveyer, each of said driving units mcludin means responsive to an increase in the driving load p aced upon it be ond a redetermined amount to check its riving e ect.

2; The combination with an endless conveyer chain of a plurality of drivin units located atspaced intervals along sai .chain in driving relationship therewlth, each of said units being mounted upon a frame having limited movement in the direction of travel of said chain, and means for normally urging said frame towards the direction of travel of said chain to hold said driving unit with a predetermined driving pressure against said chain.

3. The combination with an endless conveyer chain of a plurality of driving units each having a driving member in meshing enga ment with the links of said chain, a, mova le-frame for certain of said driving units, and resilient means associated with said frame for normally holding its respective driving member with a predetermined pressure against said chain and for rovidm compensating movement of sai frame an unit relatively to said chain articular constructional examples when the driyingf6ce exerted by said drivingmember exceeds a predetermined amount.

fqThe combination with an endless conve'yer chain of a plurality of driving clu a master driving unit, asso 'ated therewith each of said units including a driv ing member in mesh engagement with the links of said chain, each of said units with the exception of said master unit including resilient means for providing compensatm movement of its respective drivmg mem r relatively to said chain when the driving force exerted by-said member exceedsa predetermined amount.

5. The combination with an endless conveyer chain of a master driving unit and a plurality o auxiliary driving units located at spaced intervals along said chain, each of said auxiliary units includin means for automaticall reducing .the riving pressure exerted y it on said chain whenever said pressure tends to exceed a predetermined maximum.

6. The combination with an endless conve er chain of a master driving unit of variable effect and a plurality of auxiliary driving units also of variable effect, located at spaced intervals along said chain and driving relationship therewith, each of sa1d auxiliary units including means for automatically reducing its speed of, rotation when the driving force exerted by it upon said chain exceeds a predetermined maximum.

7. A driving unit for an endless conveyer chain comprising a stationary support, ,a movable frame carried by said sup ort, driving means carried by said mova le frame and including a driving member in'meshing engagement with said conveyer chain and resilient means interposed between said movable frame and support whereby bodily movement of said movable frame and the driving means carried thereby can occur in a direclel tothe direction of travel .of said chain,

driving means carried by said base including a variable speed device and means operatively associated with said base and frame for reducing a variation of said variable speed device u on relative movement between said frame an base. i

9. The combination with an endless conveyer chain, of a master driving unit and a pluralit of auxiliary driving units arranged in driving relationshi with said chain at spaced intervals along its path of travel, each of said auxiliary units m'cluding pressure responsive means and a variable speeddevice operativelyassociated with said pressure onsive means for automatically effecting deceleration or acceleration respectively in 'its in- 1 agaa'mea crease'or decrease of the driving foree ex- 'ertedb said unit on said chain. v

10. e combination with anendless conveyer chain ofa master driving unit-having f means to adjust its speed and maintainit at a predetermined rate, and a plurality of auxilia-ry driving units, each including a variable speed device adapted to be set to operate at the same rate of speed as saidmaster unit, 4;

and increase the rate of speed of said auxiliary umt' In accordance with variations from a predetermined amount of the pressure exerted by said auxiliary unit upon said' chain.

, 11. A driving unit for an endless conveyer chain comprising a stationary frame, a movable frame carried-by said stationary frame, a caterpillar chain and drivin means therefor mounted on said movab e frame, said driving means includin a variable speed gear and means automatically responsive to e s eed dewoe to be 'ad usted automatically to cause.

variations in the driving effect of said caterpillar chain for varying said variable speed gear.

12. A driving unit for an endless conveyer .chain comprising a stationary frame, amovable frame carried by said stationary frame, a caterpillar cham and drivin means therefor mounted on said movab e frame," said drlving means including a variable speed gear, means automaticall responsive to variations in the driving e ect of said caterpillar chain for varying said variable speed gear, and manually operable means for setting said variable speed device in predetermined adjusted position.

13. A driving unit for an endless conveyer chain comprising astationary frame, a movable frame carried by said stationary frame, a caterpillar chain and drivin means there- 'for mounted on said movab e frame, said driving means includin a variable speed gear, means automatical y responsive to variations in the driving effect of said caterpillar chain. for varyin said variable speed gear, manually operable means for settin said variable speed device in predetermine adjusted position, and means for selectively placing said automatically responsive means into and out of operative position.

14. A driving unit for an endless conveyer ,gear, resilient means connected with said movable and stationary frames for normally holding said caterpillar chain with a predetermined pressure in driving relationship with said conveyer chain, and means operatively associated with said frames for automatically producing through said variable speed device a variation in speed of said caterpillar chain in accordance with variations from said predetermined pressure of the driving force exerted by said caterpillar chain upon said conveyer chain.

15. A driving unit for an endless conveyer chain comprising a stationary frame, a movable frame carried by said stationary frame, a caterpillar chain and driving means therefor mounted on said movable frame, said driving means including a variable speed gear, resilient means connected with said movable and stationary frames for normally holding said caterpillar chain with a predetermined pressure in driving relationship with said conveyer chain, and means operatively associated with said frames for automatically producing through said variable speed device a variation in speed of said caterpillar chain in accordance with variations from said predetermined pressure of the driving force exerted by said caterpillar chain upon said conveyer chain, and safety means for stopping said driving unit when the pressure exerted by'said caterpillar chain exceeds a predetermined amount.

16. A driving unit for an endless conveyer chain comprising a stationary frame, a movable frame carried by said stationar frame, a base secured to said stationary rame, a

caterpillar chain drive carried by said base and comprising a pair of spaced sprockets and an endless chain trained about said sprockets means for driving said sprockets, including an electric motor and a variable speed gear, pressure responsive means interposed between said frames for normally holding them in a predetermined relative position and means operatively associated with sai frames and said variable speed gear for varying the driving speed of the latter automatically in accordance with variations in the relative position of saidframes from said predetermined position.

17. A driving unit for an endless conveyer chain comprising a stationary frame, a movable frame carried by said stationary frame, a base secured to said movable frame, a caterpillar chain drive carried by said base and comprising a pair of spaced sprockets and an endless chain trained about said sprockets, means for drivin said sprockets including an electric motor an a variable speed (gear, pres sure responsive means interpose between said frames for normally holding them in a predetermined relative position, and gearing interposed between said frames and connected with said variable speed gear for changing the adjustment of said speed gear.

18. A driving unit for an endless conveyer chain comprising a stationary frame, a movable frame carried by said stationary frame, a base secured to said movable frame, a caterpillar chain drive carried by said base and comprising a pair of spaced sprockets and an endless chain trained about said sprockets, means for driving said sprockets, including an electric motor, electric switch means carried by said frames for interrupting the circuit to said motor, and pressure responsive means interposed between said frames for normally holding them in a predetermined position in which said switch means is closed.

In testimony whereof we afiix our signatures hereto.

J ERVIS B. WEBB. DUANE A. BLAIR. CHARLES A. SINK. 

